FlutterのPDF生成に、日本語を入れたい

pdf.dartを使って、領収書のPDFを生成して、表示＆ダウンロードを試みています。
その際に、PDFの中に日本語を入れたいのですが、

invalid argument(string): Contains invaild characters "領収書"

とエラーが出てきて、日本語を表示させるのに苦戦しています。
以下コードです。

dart
1import 'package:flutter/material.dart';
2import 'package:pdf/pdf.dart';
3import 'package:pdf/widgets.dart' as pw;
4import 'package:universal_html/html.dart' as html;
5
6
7class Receipt extends StatelessWidget {
8  final title = '領収書';
9
10  @override
11  Widget build(BuildContext context) {
12    
13    final pdf = pw.Document();
14    pdf.addPage(pw.Page(
15        pageFormat: PdfPageFormat.a4,
16        build: (pw.Context context) {
17          return pw.Center(
18              child: pw.Container(
19                  width: double.infinity,
20                  margin: pw.EdgeInsets.all(20.0),
21                  padding: pw.EdgeInsets.all(20.0),
22                  child: pw.Column(children: [
23                    pw.Text(
24                      'RECIEPT',
25                      style: pw.TextStyle(
26                        fontSize: 32.0,
27                        fontWeight: pw.FontWeight.bold,
28                        // color: pw.Colors.black87
29                      ),
30                    ),
31                    pw.SizedBox(height: 20.0),
32                    pw.Text(
33                      title,
34                      style: pw.TextStyle(
35                        // locale: Locale('ja'),
36                        font: ,
37                        letterSpacing: 1.5,
38                        fontSize: 14.0,
39                        fontWeight: pw.FontWeight.bold,
40                        // color: myTheme.primaryColor
41                      ),
42                    ),
43                    pw.SizedBox(height: 20.0),
44                    pw.Align(
45                      alignment: pw.Alignment.centerRight,
46                      child: pw.Container(
47                        width: 120.0,
48                        // alignment: pw.AlignmentDirectional.centerEnd,
49                        child: pw.Column(
50                          crossAxisAlignment: pw.CrossAxisAlignment.end,
51                          children: [
52                            pw.Row(
53                              mainAxisAlignment:
54                                  pw.MainAxisAlignment.spaceBetween,
55                              children: [
56                                pw.Text('No.'),
57                                pw.Text('0000'),
58                              ],
59                            ),
60                            pw.Divider(
61                              height: 1.0,
62                              thickness: 1.5,
63                              // color: myTheme.primaryColor,
64                            ),
65                            pw.SizedBox(height: 8.0),
66                            pw.Row(
67                              mainAxisAlignment:
68                                  pw.MainAxisAlignment.spaceBetween,
69                              children: [
70                                pw.Text('日時'),
71                                pw.Text('2020/12/11'),
72                              ],
73                            ),
74                            pw.Divider(
75                              height: 1.0,
76                              thickness: 1.5,
77                              // color: myTheme.primaryColor,
78                            ),
79                          ],
80                        ),
81                      ),
82                    ),
83                    pw.SizedBox(height: 20.0),
84                    pw.Row(
85                      mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
86                      children: [
87                        pw.Text(
88                          '名前',
89                          style: pw.TextStyle(
90                              fontWeight: pw.FontWeight.bold, fontSize: 16.0),
91                        ),
92                        pw.Text('様')
93                      ],
94                    ),
95                    pw.Divider(
96                      thickness: 1.5,
97                      // color: myTheme.primaryColor,
98                    ),
99                    pw.Container(
100                      width: double.infinity,
101                      padding: pw.EdgeInsets.symmetric(
102                          horizontal: 20.0, vertical: 30.0),
103                      // color: Colors.pink[50],
104                      child: pw.Text(
105                        '１１,１１１円',
106                        textAlign: pw.TextAlign.center,
107                        style: pw.TextStyle(
108                            fontSize: 16.0, fontWeight: pw.FontWeight.bold),
109                      ),
110                    ),
111                    pw.SizedBox(height: 16.0),
112                    pw.Row(
113                      mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
114                      children: [
115                        pw.Text('ただし',
116                            style:
117                                pw.TextStyle(fontWeight: pw.FontWeight.bold)),
118                        pw.Text('チャージ',
119                            style:
120                                pw.TextStyle(fontWeight: pw.FontWeight.bold)),
121                        pw.Text('として',
122                            style:
123                                pw.TextStyle(fontWeight: pw.FontWeight.bold)),
124                      ],
125                    ),
126                    pw.Divider(
127                      height: 4.0,
128                      thickness: 1.5,
129                      // color: myTheme.primaryColor,
130                    ),
131                    pw.SizedBox(height: 4.0),
132                    pw.Container(
133                      alignment: pw.Alignment.centerLeft,
134                      child: pw.Text('ご利用代金として領収いたしました。',
135                          style: pw.TextStyle(fontWeight: pw.FontWeight.bold)),
136                    ),
137                    pw.SizedBox(height: 24.0),
138                    pw.Row(
139                      mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
140                      children: [
141                        pw.Column(
142                          crossAxisAlignment: pw.CrossAxisAlignment.start,
143                          children: [
144                            pw.Text('会社名',
145                                style: pw.TextStyle(
146                                    fontWeight: pw.FontWeight.bold)),
147                            pw.Text('郵便番号'),
148                            pw.Text('住所')
149                          ],
150                        ),
151                        pw.Container(
152                          width: 80.0,
153                          height: 80.0,
154                          child: pw.Text('ハンコ'),
155                          // color: Colors.grey[200],
156                        )
157                      ],
158                    )
159                  ])));
160        }
161        )
162        );
163    final bytes = pdf.save();
164    final blob = html.Blob([bytes], 'application/pdf');
165
166    return Scaffold(
167      appBar: AppBar(),
168      body: Center(
169        child: Column(
170          children: <Widget>[
171            RaisedButton(
172              child: Text("Open"),
173              onPressed: () {
174                final url = html.Url.createObjectUrlFromBlob(blob);
175                html.window.open(url, "_blank");
176                html.Url.revokeObjectUrl(url);
177              },
178            ),
179            RaisedButton(
180              child: Text("Download"),
181              onPressed: () {
182                final url = html.Url.createObjectUrlFromBlob(blob);
183                final anchor =
184                    html.document.createElement('a') as html.AnchorElement
185                      ..href = url
186                      ..style.display = 'none'
187                      ..download = 'some_name.pdf';
188                html.document.body.children.add(anchor);
189                anchor.click();
190                html.document.body.children.remove(anchor);
191                html.Url.revokeObjectUrl(url);
192              },
193            ),
194          ],
195          mainAxisAlignment: MainAxisAlignment.center,
196        ),
197      ),
198    );
199  }
200}
201```このコード内に使われている日本語のTextが、エラーになります。
202試したことは、pw.DefaultTextStyleを使用してみたり(同じエラーが出て効果無し)

pw.DefaultTextStyle(
child: pw.Text(
title,
),
style: pw.TextStyle(
letterSpacing: 1.5,
fontSize: 14.0,
fontWeight: pw.FontWeight.bold,
// color: myTheme.primaryColor
),
),

GoogleFontのパッケを使ってみたりしました。

pw.Text(
title,
style: pw.GoogleFonts.lato(),
),

> The name 'GoogleFonts' is being referenced through the prefix 'pw', but it isn't defined in any of the libraries imported using that prefix.
Try correcting the prefix or importing the library that defines 'GoogleFonts'